Cycloalkane Metathesis Using a Bi-Metallic System: Understanding the Effect of Second Metal in Metathesis Reaction

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Cycloalkane Metathesis using a Bi-metallic System: Understanding the Effect of Second metal in Metathesis Reaction

Thesis by

Ahmed M. Alshanqiti

In Partial Fulfillment of the Requirements For the Degree of Master of Science

King Abdullah University of Science and Technology Thuwal, Kingdom of Saudi Arabia

September, 2018

EXAMINATION COMMITTEE PAGE

The thesis of Ahmed M. Alshanqiti is approved by the examination committee.

Committee Chairperson: Prof. Jean Marie Basset

Committee Members: Kuo-Wei Huang, Prof. Pascal Saikaly

Ahmed M. Alshanqiti

ABSTRACT

Cycloalkane Metathesis using a Bi-metallic System: Understanding the Effect of Second metal in Metathesis Reaction

Ahmed M. Alshanqiti

Over the past decades, since the discovery of a single–site silica-supported catalyst for the alkane metathesis reaction by our group, we have been extensively working on the development of supported catalytic systems for the improved alkane metathesis reaction.

During these developments, we understand the reaction mechanism and reached a new perspective for the synthesis of various supported bimetallic systems via the surface organometallic chemistry (SOMC) approach. Recently, with this bi-metallic system, we got a very high TON (10000) in propane metathesis reaction. As these catalysts are very efficient for linear alkanes we thought to apply it for cyclo-alkanes specifically, for cyclooctane metathesis expecting better activity. Besides, the value of the ring alkanes are higher than the linear alkanes.

The current work demonstrates a combination of [(ΞSi−O−)W(Me)5] and [(ΞSi− O−)Ti(Np)3 pre-catalyst with several supports (SiO2-700, SBA-15 and MCM-41) for metathesis of cyclooctane. The catalysts have been synthesized and fully characterized by elemental 6 analysis (EA), FT-IR and NMR spectroscopies. After fully characterization the bi-metallic catalyst was tested for metathesis of cyclooctane with highest ever TON 2500 as compared to that of mono-metallic catalyst where we got 430 TON. Which again corroborates our prediction that bimetallic catalysts are better catalysts than monometallic catalysts.

ACKNOWLEDGEMENTS

First and foremost, I pay my gratitude to Allah, the most merciful and the mighty, for all his blessings that allowed me to accomplish this work. One of his great blessings on me was supervision of Professor Jean-Marie Basset. I would certainly like to take this opportunity to express my sincere gratitude to him. Jean-Marie is a very knowledgeable person and well-known scholars in my field. He has given me priceless advice, suggestion, and wisdom. Under his precise supervision, I have benefited immensely from his constructive criticisms, supportive mentoring skills, and continuous encouragement.

Without a doubt, this thesis would not have been possible without his help.

Special recognition and appreciation should be given to Dr. Manoja Kumar Samantary who probably was involved in many aspects of this thesis, I am so grateful to him for his insightful discussions and comments. My appreciation is also extended to Aya Saidi for her great suggestions and wise advice.

I would like to record my appreciation for the support and the cooperation received from

Basset’s group members in catalysis center KCC. It was such a pleasure to work with them.

I also would like to thank the members of my thesis examining committee, professor Kuo-

Wei Huang, and professor Pascal Saikaly, for their valuable comments and suggestions. 8

I sincerely oﬀer my profound gratitude to King Abdullah University of Science and

Technology for offering me the chance of studying and for their continued generosity. My appreciation also goes to all my colleagues and staff members who I met.

Last, but definitely not the least, I would like to express my very profound gratitude to my parents, my brothers, and sisters for the love, help, and encouragement to achieve my goals.

TABLE OF CONTENTS

EXAMINATION COMMITTEE PAGE ...... 3 COPY RIGHT PAGE …..…………………………………………………………………………………………………… 4

ABSTRACT ...... 5 ACKNOWLEDGEMENTS ...... 7 TABLE OF CONTENTS...... 9 LIST OF ABBREVIATIONS ...... 11 LIST OF ILLUSTRATIONS...... 12 LIST OF TABLES ...... 14 INTRODUCTION ...... 15

1.1. OVERVIEW OF CATALYSTS...... 15 1.1.1. Homogeneous Catalysis ...... 15 1.1.2. Heterogeneous Catalysis ...... 16 1.2. HETEROGENEOUS VS. HOMOGENEOUS CATALYSIS ...... 16 1.3. SURFACE ORGANOMETALLIC CHEMISTRY (SOMC) ...... 16 1.4. SINGLE-SITE HETEROGENEOUS CATALYST ...... 18 1.5. SOMC SUPPORTS ...... 20 1.5.1. Silica-Supported ...... 20 1.5.2. Alumina-Supported ...... 21 1.6. METATHESIS OF ALKANES ...... 22 1.7. METATHESIS OF ALKENES (OLEFINS) ...... 24 1.8. CHEMISTRY OF GROUP 5 AND 6 METALS ...... 25 EXPERIMENTS ...... 27

2.1. INTRODUCTION ...... 27 2.2. SILICA PREPARATION ...... 27

2.3. TUNGSTEN(VI) HEXAMETHYL (WME6) ...... 28

2.4. TETRA NEOPENTYL TITANIUM COMPLEX [TI(NP)4]...... 29 2.5. GRAFTING ...... 30 2.6. PROCEDURES OF METATHESIS REACTION ...... 31 10

2.7. CHARACTERIZATION OF THE SAMPLE BY INSTRUMENTS ...... 32 2.7.1. Fourier Transform Infra-Red Spectroscopy ...... 32 2.7.2. Elemental Analysis (EA) ...... 32 2.7.3. Nuclear Magnetic Resonance Spectroscopy (NMR) ...... 33 2.7.4. Gas Chromatography and Gas Chromatography-Mass Spectrometer ...... 35 RESULTS AND DISCUSSION ...... 37

3.1. INTRODUCTION ...... 37 3.2. LIQUID STATE NMR ...... 37 3.3. SOLID STATE NMR ...... 40 3.4. FOURIER TRANSFORM INFRA-RED SPECTROSCOPY (FTIR) ...... 44 3.5. ELEMENTAL ANALYSIS...... 46 3.6. CYCLOALKANE METATHESIS ...... 46 3.7. N-DECENE METATHESIS ...... 49 CONCLUSION ...... 51

4.1. OVERALL SUMMARY...... 51 4.2. CONCLUSIONS ...... 52 4.3. FUTURE WORK ...... 53 REFERENCES ...... 54

LIST OF ABBREVIATIONS

CP/MAS Cross Polarization/ Magic Angle Spinning GC Gas Chromatography GC-MS Gas Chromatography mass spectrometry h hour(s) HVL High Vacuum Line IR Infra-Red ppm Part per million mg Milligram(s) mL Milliliter(s) mol Mole(s) mmol Millimole(s) Mw Weight average molecular weight MHz Megahertz NMR Nuclear Magnetic Resonance DCM Dichloromethane Me Methyl SOMC Surface Organometallic Chemistry SOMF Surface Organometallic Fragments T Temperature TOF Turn over frequency TON Turn over number FID Flame Ionization Detector min Minute(s)

LIST OF ILLUSTRATIONS

Figure 1 Model of SOMC 4 ...... 18 Figure 2 Surface organometallic fragments (SOMF) and surface organometallic chemistry (SOMC) 4 ...... 19 Figure 3 Types of Silanols groups 7 ...... 21 Figure 4 Proposed mechanism of propane metathesis by Ta-H...... 23 Figure 5 Olefin Metathesis simple mechanism 16...... 24 Figure 6 Olefin Metathesis Mechanism by Chauvin 17 ...... 25

Figure 7 Silica SiO2-700 preparation ...... 28

Figure 8 WCl6 was sublimed under high vacuum line...... 29 Figure 9 A double schlenk flask ...... 30 Figure 10 Grafting procudure in a double schlenk flask 5...... 31 Figure 11 W(Me6) structure after successfully synthesized ...... 38 1 Figure 12 H NMR spectrum of W(Me)6 ...... 38 13 Figure 13 C NMR spectrum of W(Me)6 ...... 38

Figure 14 Ti(NP)4 structure ...... 39 1 Figure 15 H NMR spectrum of Ti(NP)4 ...... 39 13 Figure 16 C NMR spectrum of Ti(NP)4 ...... 40 Figure 17 1H single-quantum (SQ), 1H double-quantum (DQ), and 1H triplequantum (TQ)

NMR spectra of W(CH3)6 ...... 41 13 1 13 Figure 18 C CP/MAS and H− C HETCOR NMR spectrum of W(CH3)6 ...... 42 Figure 19 Grafting W and Ti on SiO2-700 (Catalyst 1) ...... 42 Figure 20 1H single-quantum (SQ), 1H double-quantum (DQ), and 1H triplequantum (TQ) NMR spectra of Catalyst 1 ...... 43 Figure 21 2D 1H and 13C (HETCOR) NMR spectrum for Catalyst 1 ...... 44 Figure 22 FTIR spectrum for silica 700 ...... 45

Figure 23 FTIR spectra of SiO2−700 (red), [(≡Si−O−)W(Me)5] (blue), and [(≡Si−O−)W(Me)5

(≡Si−O−)Ti(Np)3] (green) (catalyst 1)...... 46 Figure 24 Cyclooctane metathesis using [(≡Si−O−)W(Me)5 (≡Si−O−)Ti(Np)3] at 150 °C for 5 days ...... 47 Figure 25 Cyclooctane metathesis with monometallic catalyst based on W ...... 48 Figure 26 Cyclooctane metathesis with bimetallic catalyst based on W/Ti at MCM-41 support ...... 48 13

Figure 27 Cyclooctane metathesis with monometallic catalyst based on W at MCM-41 support ...... 49 Figure 28 Cyclooctane metathesis with monometallic catalyst based on W at SBA-15 support ...... 49 Figure 29 n-Decene metathesis with bimetallic catalyst based on W/Ti at SBA-15 support ...... 50

LIST OF TABLES

Table 1 Advantages and disadvantages of the two main types of catalysts ...... 16 Table 2 Bi-metalic on diferent support ...... 37 Table 3 Elemental analysis for (1,2 and 3) catalysts ...... 46

Chapter 1

Introduction

1. 1.1. Overview of Catalysts

Catalyst, in general, is a chemical compound or any substance that facilitate the rate of a reaction by lowering the activation energy without affecting the state of equilibrium. It is mainly divided in to three categories 1. Homogeneous 2. Heterogeneous and 3.

Enzymatic. The field of homogeneous catalysis grows a lot with time because of proper understanding of the catalyst whereas due to lack of characterization tools heterogeneous catalyst could not grow that much. In this section the advantages and dis advantages of both type of catalyst and the need of catalyst design by surface

Organometallic is important to this field will be discussed 1.

1.1.1. Homogeneous Catalysis Homogeneous catalysis describes the presence of reactant and catalyst in the same phase at either form (i.e., gas or liquid) 1. This type becomes increasingly significant for the synthesis of many industrial reactions, particularly, polymers, fine chemicals, and pharmaceutical 2.

1.1.2. Heterogeneous Catalysis Heterogeneous catalysts are usually solid while the form of reactants can be a gas or liquid. In this context, a catalyst may not necessarily exist in the same phase as the reactants as both can take different places at distinct phases. Most of the existing industrial applications of catalyst rely on heterogeneous catalyst rather than homogeneous because of their ease of use and easy separation from the reaction mixture

1.2. Heterogeneous vs. Homogeneous Catalysis

The activity, stability, selectivity, and catalyst recovery are the most prominent features that differentiate between heterogeneous and homogeneous catalyst 2. In Table 1, we provide a broad comparison between these two types in terms of their advantages and disadvantages, focusing on five characteristics (i.e., active centers, selectivity, catalyst recovery, applicability, and reaction mechanism), see the first column on the left 2,3.

Table 1 Advantages and disadvantages of the two main types of catalysts

Characteristic Homogeneous Heterogeneous Active centers All molecules Only surface atoms Selectivity Good Poor Catalyst recovery Difficult Easy Applicability Fixed Broad Reaction mechanism Defined Undefined

1.3. Surface Organometallic Chemistry (SOMC)

Industry prefer heterogeneous catalyst over molecular catalyst. The primary reason is ease of handling and easy separation from the reaction mixture 2. Additionally, it also 17 thermally more stable than molecular catalyst and reusable. Having all the advantages over molecular catalyst it mainly suffers from heterogeneity i.e the active sites are not well defined 3-4. To better understand the catalytic process if one could transfer the concept of molecular science to surface then it would be comparatively easy to draw a structure active relationship in heterogeneous catalyst. For transferring the molecular concept on to surface a new approach was developed called as Surface Organo Metallic

Chemistry (SOMC) 4. In this method a suitable organometallic fragment could attached with the surface to generate a surface organometallic fragment. In this method it is comparatively easy to follow the reaction mechanism as the SOMF is well defined. Other advantages of SOMC is the ligand as well as the surface is tunable it means you could control the steric as well as electronic properties around the metal center which in turn could enhance the catalytical properties as well as selectivity's of a given reaction 3,4 .

(Figure 1). SOMC could be considered as an innovative approach that bridge the gap between the two main types of catalysts homogeneous and heterogeneous 4,5. As it can be fully characterized by specific tools (i.e., FTIR, SS-NMR, TEM, SEM, EXAFS, XANES, UV, etc.) 4,5,6.

X= Spectator ligand Oxo, amido, imido…

M = Transition metal R = “Functional” ligand(s) W, Ta, Mo, Re… H, Alkyl, Alkylidene, Amido, Carbyne…

M’= Oxide Support

SiO2, Al2O3 , SiO2-Al2O3, SBA15, MCM 41…

Figure 1 Model of SOMC 4

1.4. Single-Site Heterogeneous Catalyst

Over the past 25 years, noticeable progress has been carried out in minimizing the gap between homogeneous and heterogeneous catalysis through SOMC approach 7. With this approach we can follow the catalytic cycle by isolating the intermediate which is comparatively difficult in homogeneous catalyst. As SOMC is an ideal approach where active sites are well-defined with uniform distribution and composition through the surface it also called as single-site heterogeneous catalyst 4,7.

• n- Alkane metathesis • Olefin metathesis • Branched alkane metathesis • Cycloalkane ISOmetathesis • Cycloolefin ROMP • Methane coupling to ethane • Cleavage Alkanes by methane • Ethylene to propylene • Ziegler-Natta • Butane to diesel Depolymerization • Hydrometathesis olefins • Alkane hydrogenolysis • Isometathesis of n-decane • Hydrogenolysis of Waxes • 1-butene to Proylene • 2-butene to propylene Metallocarbenes

Metal Hydrides Metallocarbenes Neutral / cationic Hydrides / Alkyl X = Spectator ligand

Ziegler-Natta Polymerization R = Functional Cyclotrimerization of ligand alkynes Metal Alkyls Metallocarbynes

Metathesis of Imines

Metallaziridine Metal imido Hydroamino alkylation Metalloalkoxo

Olefins Epoxidation

Figure 2 Surface organometallic fragments (SOMF) and surface organometallic chemistry (SOMC) 4

Surface organometallic catalyst can be obtained by the reaction of organometallic compound to surface. During the reaction metal can be connected to the surface by one or several bonds if it connected to a single bond it is called as monopodal complex if it connected to 2 or 3 bonds it is called as bi-podal or tri-podal complex 6. The fragment which is connected to surface through a bond called as surface organometallic fragment

SOMF 4,6. Figure 2 illustrates that many catalytic reactions, discovered by SOMC, with different coordination sphere of the grafted metal, such as metal hydride (M-H), metal alkyl (M-R) and metal imide (M-NR) 6. Therefore, the core idea of SOMC has provided 20 many advantages that comprises the optimization of the catalytic activity, and more importantly, it prevents the occurrence of bimolecular deactivation. Moreover, the catalytic activity can be altered via the ligands “molecular” fragment and the surface ligand, because they have steric properties, electronic properties, porosity, and other reasons 4.

1.5. SOMC Supports

The support is a significant part in surface organometallic chemistry to understand the support to control its reactivity and the possible structure is formed 3 . There are many types of supports available that can be used in grafting process, such as silicas, alumina, and zeolites 8,9.

1.5.1. Silica-Supported Silica is a well-known support especially used in heterogeneous catalysts. It can be amorphous/crystaline material, with a relative high surface area variable from 10 to 1000

2 1 8 10 m g- , . Silica is composed of tetrahedral SiO4 units, linked with each other in two ways, siloxane bridges, (Si–O–Si)n, and silanols, (Si–OH), as surface terminations in different types geminal, vicinal or isolate as shown in Figure 3 8. 21

Figure 3 Types of Silanols groups 8

To form uniform isolated Si-OH, dehydration and dihydroxylation process take place by treating silica at various temperature under vacuum 11,12. Treating silica at temperature around 150 °C under vacuum (10−5 mbar) results in dehydration. However, heating from

200-700 °C leads silica to partially dehydroxylated as a results SiO2−700 forms that contains

0.8 (SiOH nm−2) 11,8,12.

Mesoporous silicas have discovered for 30 years ago (OMSs) and provided materials have unique features, such as high surface area, large pore volume, uniform porosity and well- defined porous structures 11,13. For example, SBA-15 and MCM-41 are mesostructured silica with pore sizes in the range of 2–10 nm and 5–30 nm. They are prepared by using surfactant-templated to provide highly ordered hexagonal lattice with high surface areas and narrow pore size distribution 13,14.

1.5.2. Alumina-Supported

Alumina (Al2O3) is microstructure material, that has been used as a catalyst and catalyst

15 support in petroleum industries . It consists of about 25% tetrahedral AlO4 and (75%)

12 octahedral AlO6 appeared as a complex support . It forms crystalline when prepared by 22 calcination of aluminum hydroxides and oxyhydroxides at slightly high temperatures between 400 and 1000 °C as compared to silica 15. However, the bulk structure and surface sites of Alumina are still under debate 12,15.

1.6. Metathesis of Alkanes

Alkane metathesis is a reaction where a given alkane converts to its higher and lower homologue. Alkanes are often called as paraffins due to inertness towards most of the organometallic complexes. The inertness of the alkanes is because of their high bond dissociation energy of C-C and C-H bonds 3,4,6. Alkane metathesis was discovered in 1970s by Burent and Hughes where they used a bimetallic system Pt/Alumina and WO3/SiO2 as catalyst precursor for conversion of alkane and named as alkane disproportionation reaction (because of formation of lower and higher alkane) 16. In 1997 Prof. Jean-Marie

Basset synthesized a well-defined silica supported Ta-H species and used this catalyst for conversion of alkane, due to similarity of this reaction with that of olefin metathesis reaction he for the first time named it as alkane metathesis reaction as shown in figure 4

16,17. Alkane metathesis can be described by the below equation

2C2H2n+2 ⇄ Cn−iH2(n−i)+2 + Cn+iH2(n+i)+2 (Equation 1)

where 푖 = {1,2, . . . , 푛 − 1} favored for n < 4.

This reaction mainly follows 3 steps, dehydrogenation, metathesis and at the end hydrogenation. Begin with, when alkane approach towards to the catalyst precursor, C- 23

H bond activation takes place with the evolution of hydrogen and formation of metal alkyl bond. Metal alkyl can undergo α-bond metathesis to form metal carbene hydride. After

β-hydride elimination olefin results that olefin carried out olefin metathesis with metal carbene hydride resulting new olefin 17.

Ta H (n+2) < (n+1) Case of Linear Products

Ta H Ta Ta H H H Ta H Ta

Ta H CH3 Ta Ta

H2 Ta H Ta Ta 2 H CH4 C2H6 Ta H2

Figure 4 Proposed mechanism of propane metathesis by Ta-H.

The resulting new olefin can further undergo olefin metathesis/ cross metathesis to generate other new olefins or it can also undergo reduction to generate new alkanes. The selectivities in alkane metathesis purely depends upon the substituent at 1,2 or 1,3 position of the metallacycle ring 17. 24

1.7. Metathesis of Alkenes (Olefins)

Alkene metathesis (Olefin), is one of the suggested topics that has been rewarded with a

Nobel prize in 2005, by three famous scientists Yves Chauvin, Robert H. Grubbs and

Richard R. Schrock 11. It has many applications in petroleum refining and in the synthesis of pharmaceutical products. The mechanism of olefin metathesis is exchanging substituents between different alkenes, which is a [2+2] cycloaddition reactions as shown in figure 5 11,18.

Figure 5 Olefin Metathesis simple mechanism 18.

The first olefin metathesis reaction was established in 1955 by Anderson and Merckling.

They polymerized norbornene to polynorbornene by lithium aluminum tetraheptyl and titanium tetrachloride catalysts 19. In 1971, for the first time Chauvin has proposed a mechanism that explain how exactly the metathesis reaction works. He introduced this mechanism with Self-Metathesis of propylene to ethylene and 2-Butene, as shown in figure 6 19. 25

Figure 6 Olefin Metathesis Mechanism by Chauvin 19

Coperet and Basset et al. in 2001 showed the first well-defined highly active catalyst for

19 olefin metathesis supported by silica 700 [ ΞSiO−Re(ΞC−Bu-t) (ΞCH− Bu-t)(CH2Bu-t)] .

The topic of olefin metathesis is still under study, which requires more work for understanding in more details the underline difficulties of catalytic systems and their mechanism.

1.8. Chemistry of Group 5 and 6 metals

Groups 5 and 6 supported-metals are favorable for alkane metathesis owing to their electro deficient nature, and they show high reactivity and exhibit a better lifetime of the

11 catalysts . For example, a well-defined Tungsten pentamethyl grafted on SiO2-700 [(≡Si-

O-)WMe5] shows a high activity and very stable towards metathesis reaction of 26 cyclooctane and n-decene at reasonable temperatures around 150 oC 20,21. Hence, in our approach, we consider the comparison between well-defined silica-supported

monometallic (≡Si−O−)W(Me)5 to that of bi-metallic [(≡Si−O−)W(Me)5 (≡Si−O−)Ti(Np)3] on different types of silica-support.

Chapter 2

Experiments

2. 2.1. Introduction

In this chapter, we would discuss the procedures of all experiments as well as the analytical methods that have been considered in the Surface Organometallic Chemistry

Lab. These procedures depend basically on synthesis catalyst and treatment silica that use the standard Schlenk, high vacuum line, and glove box techniques.

2.2. Silica Preparation

Degussa Aerosil silica SiO2-700 is prepared under high vacuum at 700 ᵒC to give very fine white solid particles with a specific surface area roughly 200 m2/g as the same steps shown in figure 7. A mixture of Aerosil silica and enough water were placed in an oven at

120 ᵒC for 7 days, which led to from large agglomerates (250−400 μm in size). This step is very important to remove organic impurities and also to promote rehydroxylation process. In the dihydroxylation process, around 5.2 gm of dry silica was taken inside the quartz reactor and placed in the oven in two phases. initially, the reactor was heated at

150 ᵒC for 3 hours under open air, then, it reheated at 700ᵒC under high vacuum (< 10-5 28 mbar) for 24 hours. At the end, the silica SiO2-700 was cooled to room temperature and stored in a glovebox 11.

Figure 7 Silica SiO2-700 preparation

2.3. Tungsten(VI) Hexamethyl (WMe6)

The synthesis of Tungsten(VI) Hexamethyl (WMe6) is obtained from commercially available tungsten (VI) hexachloride (WCl6) in alkylation reactions with Zn (CH3)2, see

(Equation 2) 20.

WCl6 + 3 Zn(CH3)2 W(CH3)6 + 3 ZnCl2 (Equation 2)

The first step was the sublimation of WCl6 under high vacuum several times to remove organic impurities is illustrated in Error! Reference source not found. 8. Around 1.8 gm o f WCl6 has been weighted in glovebox and transferred to a double Schleck. To that, 25 mL of dry/degassed CH2Cl2 was added and cooled the mixture to -75 ᵒC. 14 mL (3 equivalent) of a mild alkylating agent Zn(CH3)2 was added drop by drop to the reaction mixture and 29 further maintain the reaction mixture at -75 ᵒC for 3 hours. Then, the mixture was warmed up to ( −35 ᵒC - 40 ᵒC) and let the reaction mixture to run at that temperature for another

50 minutes. Finally, the red-brown solid of W(CH3)6 (0.125g) was obtained after several filtrations and washing process.

Figure 8 WCl6 was sublimed under high vacuum line

2.4. Tetra Neopentyl Titanium Complex [Ti(Np)4]

Tetra neopentyl titanium complex [Ti(Np)4] is synthesized according to the procedure in the literature 22. A pentane solution of 50 gm (32.5 mmol) of neopentyl lithium was added to a pentane solution of Ti(OEt)4 1.5 mL (7.3 mmol) in a foil-covered flask. The reaction temperature was maintained at -78 °C for 3 hours. The temperature of the reaction 30 mixture was increased slowly to 25 °C and maintained at that temperature for 6 hours.

After the completion of the reaction the light brown colored substance was obtained after filtration and removal of solvents under vacuum. Finally, the light brown filtrate is sublimated for 10 hours at 55 °C (10-3 Torr) to get pure yellow crystals 22.

2.5. Grafting

The grafting process of many metal complex onto a surface of silica requires careful conditions. Because most of the metal complexes are sensitive to the air and water.

Therefore, a grafting process achieves by using either a glovebox or a Schlenk technique

11.

Figure 9 A double schlenk flask

The grafting procedure in the glove box is the same for all metallic precursor, starting with a double-Schlenk ﬂask (figure 9) that has a filter between the arm. This producer is illustrated in figure 10. An organometallic complex and pentane as solvent are added in one side of the double Schlenk while the silica sits at the other side. The grafting reaction occur by mixing the organometallic precursor to silica. After a certain interval of reaction time of metallic precursor with silica the reaction mixture was filtered and washed 3 times 31 with (20mL X 3) pentane to remove extra amount of organometallic precursor. After removal of the excess of metallic precursor from the reaction mixture the solid silica was dried under vacuum to obtain the metal grafted complex. Finally, the product is collected and characterized by IR, gas quantification methods, SS-NMR, etc 11.

Figure 10 Grafting procudure in a double schlenk flask 11.

2.6. Procedures of Metathesis Reaction

The same procedures were used for all the metathesis reaction in batch reactor condition using SOMC catalyst. The reaction is started using an ampule filled with the catalyst (20 mg) inside a glovebox. Then, the ampule with the catalyst is transferred to another glovebox to fill the reactant (1 mL of purified cyclooctane). The mixture was taken out from the glove box and vacuum sealed by freezing the reaction mixture in liquid nitrogen.

The reactor then heated at 150°C for 9 days after immersed in an oil bath. The reaction is quenched by adding 2 mL of dichloromethane (CH2Cl2) and analyzed by GC and GC-MS.

At last, the reaction is filtered and analyzed by both. 32

2.7. Characterization of the sample by Instruments

After synthesis of the SOMC complex the primary goal is to characterize the sample using modern analytical tools. This journey includes instruments like Infra-red (FTIR), Elemental

Analysis (EA), and both liquid and solid-state NMR, Gas Chromatography (GC) etc.

2.7.1. Fourier Transform Infra-Red Spectroscopy FT-IR spectroscopy was used through dehydroxylation and grafting process to study the surface modification (OH groups) of the silica support. FT-IR spectra were recorded on a

Nicolet 6700 FT-IR spectrometer that was provided with a DRIFT cell equipped with CaF2 windows. The IR samples were prepared in a glove box by using FT-IR cell, then the spectra were obtained. For each spectrum, 16 scans in the range 4 cm-1 were recorded, with a resolution of 4 cm-1.

2.7.2. Elemental Analysis (EA) Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) is an analytical technique used to determine the quantity and quality of heavy metals. In this work, ICP-

OES is used after grafting to determine the quantity of the metal that present in the solid supported complex.

2.7.3. Nuclear Magnetic Resonance Spectroscopy (NMR) NMR is a useful tool to identify organic/organometallic complex structure.. After the synthesis, our organometallic complexes are characterized by NMR in both states liquid and solid. All the samples are prepared inside the glove box under argon atmosphere.

Liquid state nuclear magnetic resonance spectroscopy the spectra in liquid-State NMR were recorded on a Bruker Avance 600 MHz spectrometer and the chemical shifts were measured relatively to the residual 1H or 13C resonance in

1 13 the both deuterated solvents CD2Cl2 (5.32 ppm for H and 53.5 ppm for C) and C6D6 (7.16 ppm for 1H and 128.06 ppm for 13C).

Solid-state Nuclear magnetic resonance spectroscopy

Similarly, one dimensional (1D) 1H MAS, 13C and 29Si CP/MAS solid state NMR spectra were recorded on Bruker AVANCE III spectrometer operating at 600 MHz resonance frequency for 1H utilized a 3.2 mm double resonance probe. 29Si NMR solid state NMR was recorded using a 400 MHz Bruker AVANCE III spectrometer with a conventional double resonance

4 mm CP/MAS probe. In all cases the samples were packed into rotors under inert atmosphere inside glove boxes. Dry nitrogen gas was utilized for sample spinning to prevent degradation of the samples. NMR chemical shifts are reported with respect to the external references TMS and adamantane. For 13C and 29Si CP/MAS NMR experiments, the following sequence was used: 900 pulse on the proton (pulse length 2.4 s), then a cross-polarization step with a contact time of typically 2 ms, and finally acquisition of the

13C and 29Si NMR signal under high power proton decoupling. The delay between the 34 scans was set to 4 s to allow the complete relaxation of the 1H nuclei and the number of scans ranged between 3 000 - 25 000 for 13C, 30 000 - 50 000 for 29Si and was 8 for 1H. An exponential apodization function corresponding to a line broadening of 80 Hz was applied prior to Fourier transformation

Two-dimensional (2D) 1H-13C heteronuclear correlation (HETCOR)

Two dimensionals solid state NMR spectroscopy experiments were conducted on a Bruker

AVANCE III spectrometer operating at 600 MHz resonance frequency for 1H using a 3.2 mm MAS probe. The experiments were performed according to the following scheme:

13 13 900 proton pulse, t1 evolution period, CP to C, and detection of the C magnetization under TPPM decoupling. For the cross-polarization step, a ramped radio frequency (RF) field centered at 75 kHz was applied to the protons, while the 13C channel RF field was matched to obtain optimal signal. A total of 64 t1 increments with 4 000 scans each were collected. The sample spinning frequency was 10 kHz. Using a short contact time (0.2 ms) for the CP step, the polarization transfer in the dipolar correlation experiment was verified to be selective for the first coordination sphere about the tungsten, that is to lead to correlations only between pairs of attached 1H-13C spins (C-H directly bonded). Using longer contact times (5 ms), we found that is possible to observe extra correlation peaks, which arise from longer-range dipolar interactions (e.g., to non-bonded protons).

1H-1H multiple-quantum spectroscopy

Two-dimensional double-quantum (DQ) and triple-quantum (TQ) experiments were recorded on a Bruker AVANCE III spectrometer operating at 600 MHz with a conventional double resonance 3.2 mm CP/MAS probe, according to the following general scheme: excitation of DQ coherences, t1 evolution, z-filter, and detection. The spectra were recorded in a rotor synchronized fashion in t1 by setting the t1 increment equal to one rotor period (45.45 µs). One cycle of the standard back-to-back (BABA) recoupling sequences was used for the excitation and reconversion period. Quadrature detection in w1 was achieved using the States-TPPI method. A MAS frequency of 22 kHz was used. The

90° proton pulse length was 2.5 µs, while a recycle delay of 5 s was used. A total of 128 t1 increments with 128 scans per each increment were recorded. The DQ frequency in the w1 dimension corresponds to the sum of two single quantum (SQ) frequencies of the two coupled protons and correlates in the w2 dimension with the two corresponding proton resonances. The TQ frequency in the w1 dimension corresponds to the sum of the three

SQ frequencies of the three coupled protons and correlates in the w2 dimension with the three individual proton resonances. Conversely, groups of less than three equivalent spins will not give rise to diagonal signals in this spectrum.

2.7.4. Gas Chromatography and Gas Chromatography-Mass Spectrometer Gas chromatography (GC) is used in analytical chemistry for separating and quantifaying complex molecules. Gas chromatography column with a split injector coupled with a FID

(Flame Ionization Detector). A HP-PLOT Al2O3 KCl 30 m × 0.53 mm; 20.00 mm capillary 36 column coated with a stationary phase of aluminium oxide deactivated with KCl was used with helium as the carrier gas at 32.1 kPa. Each analysis was carried out with the same conditions: a flow rate of 1.5 mL/min and an isotherm at 80 °C.

GC measurements were performed with an Agilent 7890A Series (FID detection). Method for GC analyses: Column HP-5; 30m length x 0.32mm ID x 0.25 μm film thickness; Flow rate: 1 mL/min (N2); split ratio: 50/1; Inlet temperature: 250 °C, Detector temperature:

250 °C; Temperature program: 40°C (3 min), 40-250 °C (12 °C/min), 250 °C (3 min), 250-

300 °C (10 °C/min), 300 °C (3 min). For cyclooctane metathesis reaction, GC response factors of available cC5-cC12 standards were calculated as an average of three independent runs. The plots of response factor versus cyclic alkane carbon number were determined and a linear correlation was found. Then, we extrapolated the response factors of this plot for the other cyclic alkane. Similarly, GC response factors of available

C7-C10 n-alkanes standards were calculated as an average of three independent runs. The plot of response factor versus n-alkanes carbon number was determined and a linear correlation was found, then we extrapolated the response factors for other n-alkanes, n- decane retention time: tR = 9.6.

GC-MS measurements were performed with an Agilent 7890A Series coupled with Agilent

5975C Series. GC/MS equipped with capillary column coated with none polar stationary phase HP-5MS was used for molecular weight determination and identification that allowed the separation of hydrocarbons according to their boiling points differences. 37

Chapter 3

Results and Discussion

3. 3.1. Introduction

This chapter reviews the main results obtained by conducting experiments that are elaborated in Chapter 2. In general, the metathesis of cyclooctane has been recorded using a bi-metallic catalyst on various supports and compared it with previously reported

[(ΞSi−O−)W(Me)5] Table 2. Additionally, the catalyst has been synthesized and fully characterized by FTIR, NMR, Elemental Analysis (EA), GC and GC-MS.

Table 2 Bi-metalic on diferent support

Bi-Metallic Catalyst Kind of support Abbreviation SiO2-700 1 [(ΞSi−O−)W(Me)5] and [(ΞSi− O−)Ti(Np)3 SBA-15 2 MCM-41 3

3.2. Liquid state NMR

Liquid state NMR was done for both the metallic precursors to make sure their purity.

1 After successfully synthesized of WMe6 the complex was fully characterized by ( H and

13 1 C) NMR (figure 11, 14). The H spectra of WMe6 has represented in Figure 12, where the

13 peak at 1.65 ppm corresponds to CH3 and in C a sharp peak was obtained at 82 ppm corresponding to CH3, of W(CH3)6 respectively Figure 13. 38

Figure 11 W(Me6) structure after successfully synthesized

1 Figure 12 H NMR spectrum of W(Me)6

13 Figure 13 C NMR spectrum of W(Me)6

1 In Figure 15 the H spectra of Ti(Np)4 has appeared, where the peak at 1.19 ppm

13 corresponds to CH3 and at 2.2 to CH2. In C peaks ware obtained at 37.6 ppm and

119.6 corresponding to CH2, and [-C- Neo pentane] of Ti(Np)4 respectively Figure 16.

Figure 14 Ti(NP)4 structure

1 Figure 15 H NMR spectrum of Ti(NP)4

13 Figure 16 C NMR spectrum of Ti(NP)4

3.3. Solid state NMR

1 Solid-state NMR was also recorded for W(CH3)6 after grafting. The H MAS/NMR spectrum

(single-quantum (SQ)) exhibit a signal at 2 ppm with correlates in both double-quantum

(DQ) and triple-quantum (TQ) dimension as shown in Figure 17. These two correlation peaks at 4 and 6 ppm, respectively, are corresponded to (-CH3) groups bonded to tungsten

(W). 41

Figure 17 1H single-quantum (SQ), 1H double-quantum (DQ), and 1H triplequantum (TQ) NMR spectra of W(CH3)6

Furthermore, the 13C CP/MAS NMR spectrum exhibit one peak at 82 ppm correlates with

1 H NMR peak at 2.0 ppm, see Figure 18. The synthesis of WMe6 was confirmed by both

1H and 13C in liquid and solid-state NMR. Furthermore, HETCOR spectra corroborates with the results obtained from 1H and 13C spectra that the synthesis of W(CH3)6 was obtained on support. 42

13 1 13 Figure 18 C CP/MAS and H− C HETCOR NMR spectrum of W(CH3)6

Solid-state NMR was recorded for bi-metallic [(ΞSi−O−)W(Me)5] and [(ΞSi− O−)Ti(Np)3]

1 supported on SiO2-700 (Catalyst 1) as shown in figure 19. The H MAS/NMR spectrum of catalyst 1 in figure 20 shows two peaks at 2.0 and 0.9 ppm which are corresponded to (-

CH3) groups of tungsten (W) and titanium (Ti). In double-quantum (DQ) and triplequantum (TQ) strong autocorrelation signals were obtained at 1.8 and 4.0 ppm (DQ) and

2.7 and 6.0 ppm (TQ) respectively.

Figure 19 Grafting W and Ti on SiO2-700 (Catalyst 1) 43

Figure 20 1H single-quantum (SQ), 1H double-quantum (DQ), and 1H triplequantum (TQ) NMR spectra of Catalyst 1

Moreover, the 13C MAS (CP/MAS) NMR spectrum presents 4 peaks at 82, 113, 36, 32 ppm which refer to (W− CH3), (Ti−CH2), (Ti−CH2−C(CH3)3), and (Ti−CH2−C(CH3)3) respectively as shown in Figure 21, which are correlated with 2D 1H and 13C (HETCOR) NMR spectrum at

2.0, 2.2, and 0.9 ppm refer to (W−CH3), (Ti−CH2), and (Ti−CH2−C(CH3)3) respectively. 44

Figure 21 2D 1H and 13C (HETCOR) NMR spectrum for Catalyst 1

3.4. Fourier Transform Infra-Red Spectroscopy (FTIR)

FTIR was used in the preparation of the silica 700 support and after grafted the complex.

In figure 22 FTIR spectrum was performed for silica 700 and shows that intense sharp band at 3747 cm−1 which refers to the (OH) stretching of the germinal silanol groups. In

cm−1 addition, wide peaks at 1980, 1850, and 1625 refers to the SiO2 network. 45

Figure 22 FTIR spectrum for silica 700

The FTIR spectrum of catalyst 1 was recorded after grafting. In Figure 23, the Spectrum shows that new bands appear in the region of 3021−2787 cm−1 and at 1465 and 1365 cm−1 which are referred to ν(CH) and δ(CH) of the methyl and neopentyl ligands bonded to tungsten and titanium, respectively. In addition, no bands appear at 3744 cm−1, which are connected with isolated and geminal silanols. 46

Figure 23 FTIR spectra of SiO2−700 (red), [(≡Si−O−)W(Me)5] (blue), and [(≡Si−O−)W(Me)5 (≡Si−O−)Ti(Np)3] (green) (catalyst 1).

3.5. Elemental Analysis

Elemental analysis has been used for catalysts 1, 2, and 3 to approve their structure Table

3 shows a summary of the elemental analysis for each catalyst.

Table 3 Elemental analysis for (1,2 and 3) catalysts

Catalyst %M 1 0.37 % 2 0.8 % 3 0.9 %

3.6. Cycloalkane Metathesis

The cyclooctane metathesis reaction was carried out in a batch reactor at 150 °C for 9 days using three catalysts (1, 2, and 3). We choose the cyclooctane to compare the reactivity of already reported catalyst to that of newly synthesized W-Ti bimetallic system 47

20,23,24. As it is known that the bi-metallic catalysts are very effective for propane metathesis we thought to imply it to see the effect of second metal on cyclooctane metathesis reaction. All the reactions were carried out following the same way: an ampoule is filled with the catalyst (20 mg, W loading: 0.37 %, 0.8% and 0,9%wt) in a glove box and the cyclic alkane (1.0 mL, 7.4 mmol) is then added. The ampoule is sealed under vacuum, immersed in an oil bath and heated at 150 °C. At the end of the reaction, the ampoule is allowed to cool to -78 oC. Then, the mixture is diluted by addition of dichloromethane and after filtration the resulting solution is analyzed by GC and GC/MS.

For kinetic studies, each analysis represents an independent run.

Indeed, the silica supported catalyst 1 shows very promising reaction in cyclooctane metathesis reaction with very high TON (2553) in only 5 days. as shown in figure 24. While,

20 in figure 25, mono-metallic system by [≡SiO-W(CH3)5] shows less TON (450) in 190 h .

Figure 24 Cyclooctane metathesis using [(≡Si−O−)W(Me)5 (≡Si−O−)Ti(Np)3] at 150 °C for 5 days

TON = 450

Figure 25 Cyclooctane metathesis with monometallic catalyst based on W

In case of SBA-15 and MCM-41 mesoporous silicas (catalyst 2 and 3 respectively), catalyst

3 was a highly active (TON= 3605) as shown in figure 26, comparing with monometallic based on W (TON=197) as shown in figure 27 23. On the other hand, and surprisingly catalyst 2 did not show any activity even after repeating reaction several times, while monometallic has shown better activity with (TON= 462) presented in figure 28 23.

Cyclooctane metathesis using W/Ti @ MCM at 150 °C for 15 days 1.20 1.00 1 day 0.80 3 day 0.60 TON=3605 5 day 0.40 9 day 0.20 15 day

0.00

C3 C4 C5 C6 C7 C9

C15 C10 C11 C12 C13 C14 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 mmolsof Cycloalkanes Cycloalkanes

Figure 26 Cyclooctane metathesis with bimetallic catalyst based on W/Ti at MCM-41 support

Figure 27 Cyclooctane metathesis with monometallic catalyst based on W at MCM-41 support

Figure 28 Cyclooctane metathesis with monometallic catalyst based on W at SBA-15 support

3.7. n-Decene Metathesis

The same procedure in cyclooctane metathesis was performed in n-Decene metathesis reaction over catalyst 2 for 9 days. The purpose to do this reaction to study the activity of the catalyst 2 after did not show any activity toward cyclooctane metathesis. As we expected the catalyst 2 exhibited a high activity toward n-decene metathesis (TON=2442). 50

In addition, the different alkane distributions obtained ranging between cC3 and cC30 are presented in figure 29.

n-decene metathesis using W/Ti @ SBA-15 at 150 °C for 0.20 9 days 0.18 0.16 0.14 0.12 1 day 0.10 3 day 0.08 TON=2442 0.06 5 day 0.04 mmolsof Cycloalkanes 7 day 0.02 9 day

0.00

C3 C4 C5 C6 C7 C8 C9

C15 C19 C11 C12 C13 C14 C16 C17 C18 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 Cycloalkanes Figure 29 n-Decene metathesis with bimetallic catalyst based on W/Ti at SBA-15 support

Chapter 4

Conclusion

In this final chapter, we outline the main contributions presented in the thesis. Firstly, we will give a summary of the thesis structure followed by a brief conclusion of the experiments. Then, we will give a possible thought to extend our research in the future.

4.1. Overall Summary

The ultimate aim of the work, presented in the thesis, was on the development of supported catalytic systems for the improved cyclo-alkane metathesis reaction via the surface organometallic chemistry (SOMC) approach. For the organization, we have structured this thesis into three chapters, starting with a general introduction on heterogeneous and homogeneous catalysis in Chapter 1. In Chapter 2, we have introduced our conducted experiments, explaining in detail the analytical methods that have been considered in the Surface Organometallic Chemistry Lab. These experiments rely on synthesis catalyst and treatment silica that use the standard Schlenk, high vacuum line, and glove box techniques. Then, in Chapter 3, we have discussed the main obtained outcomes from the conducted experiments. 52

4.2. Conclusions

Aims

The following surface organometallic chemistry, the current work exhibits

[(ΞSi−O−)W(Me)5] and [(ΞSi− O−)Ti(Np)3 pre-catalysts with several supports (SiO2-700, SBA-15 and MCM-41), which have been synthesized and fully characterized by elemental analysis (EA), FT-IR and NMR spectroscopies. Then, these catalysts have showed very efficient for linear and cycloalkanes.

Findings

We can list the main ﬁndings of our research as follows:

• We revealed that catalyst 1 and 3 (supported by SiO2-700 and MCM-41 respectively) have shown a high activity for cyclooctane metathesis reaction in comparison with monometallic by W, that leads to being less efficient than bimetallic system. • Catalyst 2 (supported by SBA-15) has never shown any activity toward cyclooctane metathesis reaction. However, it showed a high activity to linear alkanes via n- decene metathesis reaction. • We have proofed within the scope of this project that the bimetallic system exhibited a high activity in different reactant, which is unlike monometallic that always being in less activity.

4.3. Future work

There are many directions where the presented work can be extended, one of which is the investigation and understanding different metals instead of using tungsten (W) such as, molybdenum (Mo) and tantalum (Ta) in both mono and bi metallic system. Comparing their outcomes with the results obtained from this research is one our interests that I consider doing in my PhD-research.

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